1. Field of the Invention
The present invention relates to a process for producing a chromium-based fluorination catalyst, the obtained fluorination catalyst or catalyst precursor and a fluorination process and more particularly to a process for producing a chromium-based fluorination catalyst which can be used in the production of a halogenated hydrocarbon by a fluorination reaction of a halogenated hydrocarbon having 1 to 4 carbon atoms in a gaseous phase, the obtained fluorination catalyst and a process for fluorinating a halogenated hydrocarbon using said catalyst. Especially, the present invention aims to provide a process for producing a catalyst which can exhibit high activity and selectivity and is useful for the production of hydrofluorocarbons (abbreviated to "HFC") and hydrochlorofluorocarbons (abbreviated to "HCFC") which, in recent years, have been mass-produced as alternative flons.
2. Description of the Related Art
The process for producing a halogenated hydrocarbon containing fluorine from a halogenated hydrocarbon having 1 to 4 carbon atoms and hydrogen fluoride is roughly classified into a gaseous phase process and a liquid phase process. In recent years, a problem of the degradation of the ozone layer by chlorofluorocarbons (abbreviated to "CFC") having in their molecules a chlorine atom(s) has become brought to the fore, and HCFC having hydrogen in its molecule and HFC not having chlorine in its molecule have been proposed as alternatives for CFC (hereinafter referred to as "alternative flons"), and some of them have been already mass-produced. A gaseous phase process is a particularly promising process for the production of these alternative flons. In the gaseous phase process, the selection of the catalyst is important, and various catalysts have been proposed for this purpose up to now.
In patents, various metals such as Cu, Ag, Na, Cd, Ca, Zn, Hg, V, Sb, Mn, Fe, Ni, Co and Pt, for example, in the form of halides supported on activated carbon, are described to be useful as the catalyst (see U.S. Pat. No. 2005707). In many cases, however, a catalyst composed mainly of an oxide, fluoride or oxyfluoride of chromium or a halide of aluminum, iron or other metals is generally used. Especially, it is most common to use a catalyst comprising a chromium oxide, and many production methods and compositions have hitherto been proposed for the chromium oxide catalyst.
Japanese Examined Patent Publication (Kokoku) No. 39-10310 proposes a Cr.sub.2 O.sub.3 catalyst produced by imprenating alumina with chromic(VI) acid, drying the impregnated alumina and subjecting the dried impregnating Cr (VI) to reduction with hydrogen. Japanese Examined Patent Publication (Kokoku) No. 41-203 describes that a black chromium oxide having an atomic ratio of O to Cr in the range of from 1.5 to 3 produced by repeating several times firing in an oxygen atmosphere and firing in a hydrogen atmosphere and finally carrying out firing in an oxygen atmosphere has a high activity. Further, Japanese Examined Patent Publication No. 42-3004 discloses a Cr.sub.2 O.sub.3 catalyst produced by firing hydrous chromium oxide, which has been prepared from a chromium(III) salt solution by the precipitation process, in an atmosphere comprising water vapor and an inert gas at 300.degree. to 400.degree. C.
In recent years, Japanese Unexamined Patent Publication (Kokai) No. 5-146680 describes that a catalyst prepared in the same manner as described in Japanese Examined Patent Publication (Kokoku) No. 42-3004, that is, a chromium oxide having a specific surface area of not less than 170 m.sup.2 /g prepared by firing a chromium hydroxide, which has been prepared by the precipitation process, in a N2 gas stream at 380.degree. to 460.degree. C. has a high activity.
The present inventors have already found that the selection of heat treatment conditions is important at the time of regeneration of a Cr-based fluorination catalyst. Specifically, as described in Japanese Unexamined Patent Publication (Kokai) No. 5-92141, the activity of the catalyst can be restored sufficiently without scattering of Cr by heat-treating the catalyst first with an oxidizing gas, such as O.sub.2, and then with a reducing gas, such as H.sub.2.
However, when HCFC and HFC each containing in its molecule a hydrogen atom, which have been proposed as alternative flons, are produced by reacting a halogenated hydrocarbon with hydrogen fluoride, the reaction does not proceed smoothly in many cases as compared with the reaction in the production of the conventional CFC. In this case, in order to attain a satisfactory yield using the conventional chromium-based fluorination catalyst, the reaction should be carried out at a high temperature of 350.degree. C. or above. Further, in the production of a halogenated hydrocarbon having hydrogen in its molecule, the deposition of carbon on the catalyst is so significant that a deterioration in catalytic activity is likely to be accelerated (see Japanese Examined Patent Publication (Kokai) No. 1-262946).
Since the rate of deterioration in catalytic activity increases with increasing the reaction temperature, a reaction at a low temperature using a catalyst having a high activity contributes to thermal energy saving and, at the same time, significantly benefits the catalyst life. For this reason, in order to produce HCFC and HFC with a high efficiency, there are demands for catalysts superior to the conventional fluorination catalyst in catalytic activity and life.
An object of the present invention is to provide a process for producing a chromium-based fluorination catalyst useful for the production of HCFC and HFC and a process for producing a halogenated hydrocarbon having in its molecule a hydrogen atom(s) and a fluorine atom(s) with a high efficiency by fluorinating a halogenated hydrocarbon having 1 to 4 carbon atoms in a gaseous phase using said catalyst.